Motor vehicles typically use a mechanical differential to distribute engine torque between paired left and right drive wheels. A differential allows paired left and right drive wheels driven by the same input to rotate at different speeds. As compared with a solid axle, this provides superior handling during cornering by allowing the inside drive wheel to turn more slowly than the outside drive wheel. A conventional rear differential is located underneath a car in the middle between the back tires. A differential is a group of gears that revolve around each other and let the two tires, the laterally paired left and right tires, travel at different speeds. A differential is really important for vehicle handling when going around corners, because the tire on the inside of the turn is going in a smaller circle than the outside and therefore is going slower. Without a differential one tire would be dragging, and the car would be difficult to turn and would want to keep going straight. The drawback of a differential is that it causes the vehicle to have less traction because it lets one tire spin without the other and allows the drive force to automatically go to the drive wheel with the least traction.
The reason we need differentials has not changed, but modern higher performing vehicles sometimes need more traction, so in the prior art traction adding devices have been added to try to compensate for the differential.
Some vehicles use limited slip differentials that limit the amount of torque supplied to an idly rotating drive wheel, such as may occur when wheel traction is lost. In vehicles with limited slip differentials, the drive torque applied to the inner drive wheel produces a moment counteracting the moment which tends to turn the motor vehicle. As a result, turning performance with a limited slip differential is lowered as compared with an open differential.
In some circumstances, such as may occur in off-road driving, it is desirable that left and right drive wheels turn in unison regardless of the traction (or lack thereof) available to either wheel individually. Some vehicles provide locked or selectively lockable differentials, which fix, permanently or selectively, the relative rotational orientations of paired left and right drive wheels.
Since open, limited-slip and locked differentials are more or less advantageous depending on circumstances, there is a desire for methods and apparatus that distribute engine torque to paired left and right drive wheels according to selectable and/or automatically adjustable modes. There is further a desire for methods and apparatus that permit the torque at which left and right drive wheels slip relative to one another to be selectively progressively or infinitely varied.
In the prior art applicants are aware of U.S. Pat. No. 7,111,702 which issued Sep. 26, 2006, to Perlick et al. Perlick describes a system for steering angle control of independent rear clutches. Perlick teaches that the vehicle must have four wheel drive and have a conventional differential as the primary drive, which is taught to be in the front end and to receive two-thirds of the power, with the remaining one third of the power going to the secondary drive, ie, to his system. Perlick also calls for a center differential and brake manipulation. In contra-distinction the apparatus described herein works in front wheel drive, rear wheel drive, four or more wheel drive, and equally well with live or independent axles. The present apparatus, that is, as described herein, does not need a primary drive, or as described by Perlick, a conventional front differential, and in fact does not need a conventional differential at all, but will work equally well in conjunction with one. The apparatus described herein can be a stand alone two wheel drive, primary drive, secondary drive, or four or more wheel drive. Perlick requires a micro-processor, multiple sensors and brake manipulation, wherein the present apparatus may advantageously be controlled by the steering or by a separate actuating circuit such as a separate hydraulic circuit, or may for example, like Perlick, utilize processors and sensors.
Perlick's system is either engaged or disengaged, wherein the present apparatus is progressive from completely engaged to completely disengaged as required. According to Perlick, the primary purpose is to improve cornering in primarily front wheel drive applications and is thus not a traction device per se, whereas the present apparatus works in all applications and provides improved steering and handling performance with the least compromise in traction. Perlick teaches only regulating the back wheels and leaving the front wheels with traction and steering compromises, whereas the present application may regulate all driven wheels.
In the prior art applicants are also aware of U.S. Pat. No. 6,817,434 to Sweet which issued Nov. 16, 2004, for an Active Hydraulically Actuated On-demand Wheel End Assembly. Sweet describes a system which is normally 100% unlocked, there thus being zero traction during the normal 100% unlocked mode of each wheel end assembly.
The present apparatus is the opposite, that is, each clutch is normally 100% locked and thus starts with 100% traction. Sweet requires pressure to increase traction and drive the vehicle, whereas the present apparatus is again opposite. In an embodiment of the present apparatus which employs a hydraulic actuator, as the hydraulic system is pressurized traction is decreased only in order to steer the vehicle. Sweet teaches the reverse; viz, manipulating pressure to increase traction. The presently described system manipulates pressure to increase steering performance, whereas the Sweet system takes a wheel spinning under power and attempts to stop or slow it by applying pressure and increasing clutch friction. Typically this condition would be caused while increased power is called for during driving. The present device is the opposite as it keeps the axles locked while the largest amounts of power and traction are required, and then only releases holding force in the clutch when the vehicle is negotiating a turn. Typically this would take place only during reduced throttle applications, and so the present apparatus works in synergy with the reality of the driving dynamics: traction when power is applied, reduced or zero hold in any one independently controlled wheel clutch when handling is required and power requirements typically are reduced.
In the present apparatus a hydraulic pressure failure results in the full traction, i.e., each affected wheel clutch remains fully locked, thereby providing power and 100% traction to the wheels. In the Sweet design, if there is a pressure failure, transmitted power and traction goes to zero and the vehicle cannot move.
The present apparatus acts like a conventional vehicle when parked, i.e. the vehicle is locked in position even without use of a hand-brake. The Sweet design requires a hand-brake or the like or pressure as the wheels are unlocked when parked in the event that pressure bleeds down. Further, the Sweet design does not work on live axles, whereas the present apparatus does. In the Sweet design the axles are short, limiting wheel travel and ground clearance. In the present design longer axles may be used than currently exist, increasing wheel travel and ground clearance. The Sweet design may not easily be retro fitted to existing cars whereas in the present apparatus the wheel clutches may replace existing hubs, differentials or axles in whole or in part, and may be added to the outside of the wheel brakes as a form of locking/unlocking hub.
As with the Perlick design, the Sweet design requires complex sensors, computers or other processors (computers, processors, programmable logic controllers, etc collectively referred to as processors herein) and requires brake control first, then rear traction control followed by front traction control. The present apparatus may in one embodiment be simply controlled by the steering, advantageously with a manual over-ride to help the wheel clutches in the locked position. Unlike in the present apparatus, Sweet makes no mention of unlocking inside tires in a corner, whereas, as described herein, the present apparatus automatically unlocks the inside tires, dramatically improving performance in all conditions.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will be apparent to those of skill in the art upon a reading of the specification and a study of the drawings.